The invention relates to the preparation and use of amino-terminated polybutadienes.
Hydroxyl-terminated polybutadiene (HTPB) and hydrogenated HTPB have been commercially used in applications demanding low temperature flexibility, water resistance, hydrolytic, acid, or base stability, and/or low dielectric constant, for example in adhesives, sealants, coatings, and electrical potting insulation. However, a deficiency of using HTPB and hydrogenated HTPB is often caused by the rather weak nucleophilicity of the hydroxyl group at the chain end, which prevents its incorporation into formulations under commonly used process conditions. For example, the hydroxyl groups are usually not sufficiently reactive with bisphenol A (BPA) epoxy resins to be useful as crosslinkers or flexibilizers. In addition, when preparing electric potting compounds, the reaction rate between the anhydride of maleic anhydride (MA)-modified polybutadiene and the hydroxyl group of HTPB is too slow at room temperature. Also, the curing reaction between the hydroxyl group of HTPB and isocyanate groups in certain polyurethane applications is hindered, or is rendered incomplete, by the presence or other hydroxyl-containing additives which react at a comparable or faster rate.
Since amine groups have higher nucleophilic reactivity, the amine-terminated polybutadiene (ATPB) polymers corresponding to the HTPB polymers would have been preferable, except for the difficulty and expense of prior art methods of preparing ATPB.
Prior methods of preparing amino-terminated hydrogenated polybutadiene polymers (ATPB) have included synthesis from functionalized initiators and butadiene monomer or by converting hydroxyl-terminated polybutadiene (HTPB) to ATPB by multi-step synthetic pathways.
Lintsell, et al., Synthesis and characterization of xcex1, xcfx89- and xcex1-functionalized hydrogenated polybutadienes: telechelic and semi-telechelic amine and phosophite terminated polymers, Polymer, Vol. 38, Number 11, 2835 (1997) disclosed tosylation of primary HTPBs followed by reaction with aniline or n-propylamine or 3-(dimethylamino)-propyl amine. The terminally tosylated HTPBs were reacted with sodium azide in solvent and then hydrogenated to form the xcex1, xcfx89-diamino polymer (ATPB).
Similarly, Hinney et al., U.S. Pat. No. 4,658,062 assigned to Atlantic Richfield Company, disclosed converting liquid primary HTPB polymer such as Poly bd R45-HT brand to produce ATPB via alkane- or arenesulfonate-terminated polybutadiene. Such methods as that of Lintsell, et al., and Hinney, et al. are interesting from an academic standpoint but are too expensive and cumbersome for commercial use.
Yeakey, et al., U.S. Pat. No. 4,994,621 assigned to Texaco Chemical Company, disclosed reacting liquid HTPB polymer such as Poly bd R45-HT brand wherein the hydroxyl groups are primary, with several oxirane units per hydroxyl group, to produce a secondary hydroxyl-terminated polymer containing ether linkages. The resultant polymers were aminated by reacting ammonia with the hydroxyl groups under reducing conditions provided by hydrogen under pressure to produce a polymer which was essentially primary amine-terminated. The resultant ATPB of Yeakey, et al., was used in the preparation of polyurea foam or polyurea elastomer and to prepare more hydrophobic cured epoxy resin formulations than could be prepared with previous polyamines.
However, such prior art ATPBs suffered from one or more disadvantages. For example, such prior ATPBs containing ether groups were not weatherable and the resultant polyureas, epoxies, and other resins prepared therefrom were also not weatherable in many cases.
In a copending patent application, application Ser. No. 10/300,435 filed Nov. 19, 2002, we disclosed a method of preparing amine-terminated polybutadiene polymers having one or two terminal amine groups comprising aminating a secondary hydroxyl-terminated polybutadiene having no ether groups. In some situations, an alternative method of preparation may be desirable.
Reinking, U.S. Pat. No. 3,316,185, discloses liquid glycol diamines used as curing agents for polyepoxide compositions prepared by cyanoalkylating a glycol of the general formula HOxe2x80x94(CnH2nO)xH wherein n has a value of 2 to 5 and x has a value of 1 to 11. Hydroxyl terminated polybutadiene is not disclosed or suggested by Reinking as a suitable substance (HTPB is not a glycol) to be aminated.
It is an object of the present invention to provide ATPBs which enable improved weatherability when reacted with polyisocyanates, epoxides, anhydride functional polymers, phenolics, or multifunctional carboxylic acid or ester derivatives.
It is another object of the invention to provide ATPBs which can be used as flexibilizers, tougheners, or crosslinkers to produce cured resins with improved physical properties versus the prior ATPBs.
These objects, and others which will become apparent from the following disclosure, are achieved by the present invention which comprises in one aspect a method of preparing amine-terminated polybutadiene polymers having one or two terminal amine groups comprising aminating a hydroxyl-terminated polybutadiene by cyanoethylation followed by reduction. The cyanoethylation is carried out by a Michael addition of acrylonitrile to the terminal hydroxyl groups to form terminal cyano groups, followed by reduction with hydrogen to form terminal amine groups on the polybutadiene.
In another aspect, the invention comprises the novel amine-terminated polybutadiene polymers having one or two terminal amine groups prepared by the novel method.
The amine-terminated polybutadiene polymers having one or two terminal amine groups can be hydrogenated or partially hydrogenated, either before or after amination, if desired.
A further aspect is a method of imparting improved physical properties to epoxies, anhydride-functionalized polymers, phenolics, multifunctional carboxylic acid or ester derivatives, and the like to flexibilize, crosslink, and/or toughen the resulting polymers by curing the epoxies, anhydride-functionalized polymers, phenolics, or multifunctional carboxylic acid or ester derivatives with the novel ATPBs and/or hydrogenated ATPBs of the invention.
The resulting polymeric compositions and polymers, i.e., polyureas, polyamides, polyamic acids, polyimides, polyurethanes and reaction products with epoxies, phenolics, and anhydrides, are also an aspect of the invention. Such cured polymer products are characterized by exceptional flexibility and toughness. Moreover, the polymers produced with the novel amine-terminated polybutadiene polymers having one or two terminal amine groups possess excellent water resistance and superior, low dielectric properties.